In the packaging of integrated circuit devices, including memory devices and other integrated circuits, the use of BGA's has become increasingly popular in that they permit a very high density of inter-connections; provide a relatively low package profile; have very short lead lengths which provides improved electrical characteristics; and they may be utilized in multiple chip devices. Usually, the balls of a BGA are soldered to an array of pads on a printed circuit board for permanent connection to leads extending to other circuitry. However, in many instance, particularly during prototype debugging or bum-in, BGA's are removably placed in a socket for testing or operating
Test and bum-in BGA sockets have been available for several years. Ordinarily, these sockets include a printed circuit board having an array of electrically conductive pads on its surface. The pads match the arrangement of the balls on the BGA to be inserted. The BGA is then placed in the socket and is pressed against the array of pads by a force normal to the package itself. In order to guarantee electrical contact, the typically required pressure load applied to contacts is about 50 to 100 grams per contact. Therefore, when there are high ball counts, the mechanism to apply a uniform force is large and cumbersome. Slight variations in the size of the balls can require particularly excessive force, sufficient to bend the printed circuit board itself so as to force all of the balls into contact with the underlying pads.
In addition to the high force required with the existing test and bum-in sockets, they typically have a very large inductance, in the order of more than 10 mH per ball. This large inductance makes such sockets unsuitable for production use.